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  • 11
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    Mechanism of biological denitrification inhibition: procyanidins induce an allosteric transition of the membrane-bound nitrate reductase through membrane alteration (2016)
    Oxford University Press
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    Publication Date: 2016-04-07
    Description: Recently, it has been shown that procyanidins from Fallopia spp. inhibit bacterial denitrification, a phenomenon called biological denitrification inhibition (BDI). However, the mechanisms involved in such a process remain unknown. Here, we investigate the mechanisms of BDI involving procyanidins, using the model strain Pseudomonas brassicacearum NFM 421. The aerobic and anaerobic (denitrification) respiration, cell permeability and cell viability of P. brassicacearum were determined as a function of procyanidin concentration. The effect of procyanidins on the bacterial membrane was observed using transmission electronic microscopy. Bacterial growth, denitrification, NO 3 - and NO 2 -reductase activity, and the expression of subunits of NO 3 - (encoded by the gene narG ) and NO 2 -reductase (encoded by the gene nirS ) under NO 3 or NO 2 were measured with and without procyanidins. Procyanidins inhibited the denitrification process without affecting aerobic respiration at low concentrations. Procyanidins also disturbed cell membranes without affecting cell viability. They specifically inhibited NO 3 - but not NO 2 -reductase. Pseudomonas brassicacearum responded to procyanidins by over-expression of the membrane-bound NO 3 -reductase subunit (encoded by the gene narG ). Our results suggest that procyanidins can specifically inhibit membrane-bound NO 3 -reductase inducing enzymatic conformational changes through membrane disturbance and that P. brassicacearum responds by over-expressing membrane-bound NO 3 -reductase. Our results lead the way to a better understanding of BDI.
    Print ISSN: 0168-6496
    Electronic ISSN: 1574-6941
    Topics: Biology
    Published by Oxford University Press
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  • 12
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    On the wind contribution to the variability of ocean currents over wide continental shelves: a case study on the northern Argentine continental shelf (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The Southwestern Atlantic Ocean has one of the largest and most productive continental shelves of the southern hemisphere. Despite its relevance, its circulation patterns have been largely inferred from hydrographic observations and numerical models. Here we describe the variability of the shelf circulation based on the analysis of eleven months of multi‐level currents measured by two bottom‐mounted acoustic Doppler current profilers deployed over the continental shelf at 39°S. The record‐length mean is 12 cm s‐1 and 13 cm s‐1 in the upper layer and decreases to 6 cm s‐1 and 8 cm s‐1 near the bottom, at the deployment nearer and further from the coast respectively. The mean flow direction is towards the NE, following the orientation of the isobaths. Measurements at both sites show that the along‐shore barotropic component accounts for 83% of the variability observed and are well correlated (0.86), suggesting a relatively uniform flow, which is presumably driven by large‐scale forcing. Indeed, large scale wind stress patterns dominate the temporal variability of the in‐situ currents and the passage of atmospheric fronts induces significant changes in the observed currents at all depths. We found that for 12 % of the measurements the currents reverse the direction to the SW in response to these atmospheric patterns. Furthermore, the analysis of sea surface height reconstructed from bottom pressure measurements at both sites and from a coastal tide gauge reveals that the variability of the along‐shore currents is driven by the cross‐shore pressure gradients generated by the along‐shore wind stress.
    Print ISSN: 2169-9275
    Electronic ISSN: 2169-9291
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 13
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    Repetitive element hypermethylation in multiple sclerosis patients (2016)
    BioMed Central
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    Publication Date: 2016-06-19
    Description: Multiple sclerosis (MS) is a complex disorder of the central nervous system whose cause is currently unknown. Evidence is increasing that DNA methylation alterations could be involved in inflammatory and neuro...
    Electronic ISSN: 1471-2156
    Topics: Biology
    Published by BioMed Central
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  • 14
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    Malvinas Current variability from Argo floats and satellite altimetry (2016)
    Wiley
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    Publication Date: 2016-06-10
    Description: The Malvinas Current (MC) is an offshoot of the Antarctic Circumpolar Current (ACC). Downstream of Drake Passage, the northern fronts of the ACC veer northward, cross over the North Scotia Ridge (NSR) and the Malvinas Plateau and enter the Argentine Basin. We investigate the variations of the MC circulation between the NSR and 41°S and their possible relations with the ACC circulation using data from Argo floats and satellite altimetry. The data depict meandering and eddy-shedding of the northern ACC jets as they cross the NSR. The altimetry fields show that these eddies are trapped, break down and dissipate over the Malvinas Plateau, suggesting that this region is a hot spot for dissipation of mesoscale variability. Variations of sea level anomalies (SLA) across the NSR do not impact the MC further north, except for intra-seasonal variability associated with coastal trapped waves. Altimetry and float trajectories show events during which a large fraction of the MC is cut off from the ACC. Blocking events at around 48.5°S are a recurrent feature of the MC circulation. Over the 23 year altimetry record, we detected 26 events during which the MC surface transport at 48.5°S was reduced to less than half its long term mean. Blocking events last from 10 to 35 days and do not present any significant trend. These events were tracked back to positive SLA that built up over the Argentine Abyssal Plain. Future work is needed to understand the processes responsible for these blocking events. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 15
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    Altimeter-derived seasonal circulation on the Southwest Atlantic shelf: 27° – 43°S (2015)
    Wiley
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    Publication Date: 2015-04-17
    Description: Altimeter sea surface height (SSH) fields are analyzed to define and discuss the seasonal circulation over the wide continental shelf in the SW Atlantic Ocean (27°-43°S) during 2001-2012. Seasonal variability is low south of the Rio de la Plata (RdlP), where winds and currents remain equatorward for most of the year. Winds and currents in the central and northern parts of our domain are also equatorward during autumn and winter but reverse to become poleward during spring and summer. Transports of shelf water to the deep ocean are strongest during summer offshore and to the southeast of the RdlP. Details of the flow are discussed using mean monthly seasonal cycles of winds, heights and currents, along with analyses of Empirical Orthogonal Functions. Principle Estimator Patterns bring out the patterns of wind forcing and ocean response. The largest part of the seasonal variability in SSH signals is due to changes in the wind forcing (described above) and changes in the strong boundary currents that flow along the eastern boundary of the shelf. The rest of the variability contains a smaller component due to heating and expansion of the water column, concentrated in the southern part of the region next to the coast. Our results compare well to previous studies using in situ data and to results from realistic numerical models of the regional circulation. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 16
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    Seasonal variability and coastal upwelling near Cape Santa Marta (Brazil) (2013)
    Wiley
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    Publication Date: 2013-02-23
    Description: [1]  The Santa Marta Grande Cape (CSM) area, a relatively steep and narrow continental shelf off southeast Brazil, is under the influence of the Brazil Current and intense seasonal variations of the wind field that affect the composition of water masses and their circulation. Hydrographic data, satellite derived wind stress and numerical simulations are used to characterize the seasonal and shorter period variability of the oceanographic conditions off CSM, in the area between 27 o S and 30 o S. The study is focused on the upwelling episodes and the dynamical mechanisms associated with these events. Field data and numerical results indicate significant seasonal changes in the oceanographic structure, the water mass composition and the dynamical balance. During fall and winter, when southwesterly winds prevail and the frequency of meteorological frontal systems increases the region is characterized by waters of continental origin, the Plata Plume Water (PPW). During spring and summer deeper waters reach the surface layer due to the action of northeasterly winds. Coastal upwelling events are revealed by surface temperature minima observed south of CSM. Synoptic data show that these events occur in pulses associated with changes in the wind direction. The analysis of the numerical results show that this particular location of the upwelling band results from the synergy between shelf-break upwelling and the regional shelf circulation induced by the northeasterly winds both of which are modulated by changes in the coastline orientation and shelf width.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 17
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    Abyssal Transport Variations in the Southwest South Atlantic: First Insights From a Long‐Term Observation Array at 34.5°S (2019)
    Wiley
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    Publication Date: 2019
    Description: Abstract The zonal structure and time variability of the abyssal flow (below 3,000 dbar) in the South Atlantic western boundary is investigated using a combination of moored observations and simultaneous hydrographic/velocity sections at 34.5°S during 2009–2018. Moored direct velocity measurements near the bottom show strong variability with a peak‐to‐peak range exceeding 80 cm/s and dominant signals at times scales of 1–2 months. Daily time series of the meridional absolute geostrophic volume transport computed from the moorings reveals a highly energetic record with a temporal standard deviation of 8.3 Sv and peak‐to‐peak variations of 49 Sv, suggesting a significant contribution of the abyssal layer flows to the Deep Western Boundary Current time variability. The absolute transport is mostly driven by barotropic changes that are dominated by variations in the bottom pressure ~650 km away from the continental slope.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 18
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    Basin-Wide Oceanographic Array Bridges the South Atlantic (2014)
    Wiley
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    Publication Date: 2014-02-12
    Description: The meridional overturning circulation (MOC) is a global system of surface, intermediate, and deep ocean currents. The MOC connects the surface layer of the ocean and the atmosphere with the huge reservoir of the deep sea and is the primary mechanism for transporting heat, freshwater, and carbon between ocean basins. Climate models show that past changes in the strength of the MOC were linked to historical climate variations. Further research suggests that the MOC will continue to modulate climate change scenarios on time scales ranging from decades to centuries [ Latif et al ., 2006].
    Print ISSN: 0096-3941
    Electronic ISSN: 2324-9250
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 19
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    The salinity signature of the cross-shelf exchanges in the southwestern Atlantic Ocean: Numerical simulations (2014)
    Wiley
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    Publication Date: 2014-10-18
    Description: A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA) the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the inter-annual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 20
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    The salinity signature of the cross-shelf exchanges in the southwestern Atlantic Ocean: Satellite observations (2014)
    Wiley
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    Publication Date: 2014-10-18
    Description: Satellite derived sea surface salinity (SSS) data from Aquarius and SMOS are used to study the shelf-open ocean exchanges in the western South Atlantic near 35ºS. Away from the tropics these exchanges cause the largest SSS variability throughout the South Atlantic. The data reveal a well defined seasonal pattern of SSS during the analyzed period and of the location of the export of low salinity shelf waters. In spring and summer low salinity waters over the shelf expand offshore and are transferred to the open ocean primarily southeast of the river mouth (from 36 ºS to 37º30’S). In contrast, in fall and winter low salinity waters extend along a coastal plume and the export path to the open ocean distributes along the offshore edge of the plume. The strong seasonal SSS pattern is modulated by the seasonality of the along-shelf component of the wind stress over the shelf. However, the combined analysis of SSS, satellite-derived sea surface elevation and surface velocity data suggest that the precise location of the export of shelf waters depends on offshore circulation patterns, such as the location of the Brazil Malvinas Confluence and mesoscale eddies and meanders of the Brazil Current. The satellite data indicate that in summer, mixtures of low salinity shelf waters are swiftly driven towards the ocean interior along the axis of the Brazil/Malvinas Confluence. In winter, episodic wind reversals force the low salinity coastal plume offshore where they mix with tropical waters within the Brazil Current and create a warmer variety of low salinity waters in the open ocean.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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